Fix ImageCacheFile.__repr__ to not send signals

Cachefile strategy may be configured to generate file when file existance required.

To generate images, async backends passes `ImageCacheFile` instance to worker.
Both celery and RQ calls `__repr__` method for each argument to enque call.
And if `__repr__` of object will send `existnace_required` signal, we will get endless recursion.

Issue: #434

imagekit/cachefiles/__init__.py

@@ -3,6 +3,7 @@ from django.conf import settings
 from django.core.files import File
 from django.core.files.images import ImageFile
 from django.utils.functional import SimpleLazyObject
+from django.utils.encoding import smart_str
 from ..files import BaseIKFile
 from ..registry import generator_registry
 from ..signals import content_required, existence_required
@@ -149,6 +150,11 @@ class ImageCacheFile(BaseIKFile, ImageFile):
         # Python 2 compatibility
         return self.__bool__()
 
+    def __repr__(self):
+        return smart_str("<%s: %s>" % (
+            self.__class__.__name__, self if self.name else "None")
+        )
+
 
 class LazyImageCacheFile(SimpleLazyObject):
     def __init__(self, generator_id, *args, **kwargs):

tests/test_cachefiles.py

@@ -1,3 +1,4 @@
+import mock
 from django.conf import settings
 from hashlib import md5
 from imagekit.cachefiles import ImageCacheFile, LazyImageCacheFile
@@ -48,6 +49,31 @@ def test_no_source_error():
     file.generate()
 
 
+def test_repr_does_not_send_existence_required():
+    """
+    Ensure that `__repr__` method does not send `existance_required` signal
+
+    Cachefile strategy may be configured to generate file on
+    `existance_required`.
+    To generate images, backend passes `ImageCacheFile` instance to worker.
+    Both celery and RQ calls `__repr__` method for each argument to enque call.
+    And if `__repr__` of object will send this signal, we will get endless
+    recursion
+
+    """
+    with mock.patch('imagekit.cachefiles.existence_required') as signal:
+        # import here to apply mock
+        from imagekit.cachefiles import ImageCacheFile
+
+        spec = TestSpec(source=get_unique_image_file())
+        file = ImageCacheFile(
+            spec,
+            cachefile_backend=DummyAsyncCacheFileBackend()
+        )
+        file.__repr__()
+        eq_(signal.send.called, False)
+
+
 def test_memcached_cache_key():
     """
     Ensure the default cachefile backend is sanitizing its cache key for